Simulation in a web browser
The modifier for cloth physics exists only in Blender — there is no way to export it to any format I'm aware of. You can either set up a new physics simulation in a physics engine compatible three.js (which may give different results!) or bake your animation.
For workflows to &quot;bake&quot; the animation, see Cloth Bake: Save frames in timeline as shape key? and https://blenderartists.org/t/export-bezier-curve-animation-as-gltf-and-or-fbx/1151423/4.